Zoom magnification. 3x, 5x, 10x? What lens length gives you what?  
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Zoom magnification. 3x, 5x, 10x? What lens length give... - 2/12/2005 6:14:05 PM   
RCadmin



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Status: offline 		What are the magnification values for the various lens lengths? If I have a 200mm and 300mm for example what are their equivalent magnification values?

Also any opinions on extenders? I see Canon has 1.4x and 2.0x extenders. How do these play in to the above question and what quality or other issues do they present?

Are you sometimes better of going 200m with an extender or 300mm without?

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RE: Zoom magnification. 3x, 5x, 10x? What lens length ... - 2/12/2005 6:31:18 PM   
Tall Paul



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Joined: 6/23/2002
From: Palmdale, CA, USA
Status: offline 		Zoom typically refers to how much a given lens's focal length is changed for the zoom.
A 100 mm lens zoomed 2x is equivalent to a 200 mm lens.
on my Fuji 2600, the lens zoom is from 6 mm to 36 mm, or 6x.
This corresponds to a 38 to 228 lens in 35 mm film format, based on the image size equivalent; at 6mm the field of view is equivalent to a 38 mm in 35 mm format.
.
an extender multiplies the lens focal length by the number... 1.4 or 2.. it also does the same to the f-stop, increasing that at the same time by the same amount.
f8 becomes f 16, for instance.

< Message edited by Tall Paul -- 2/12/2005 6:33:10 PM >

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RE: Zoom magnification. 3x, 5x, 10x? What lens length... - 2/12/2005 7:21:43 PM   
RCadmin



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Status: offline 		Do these correspond to "real world" magnification values then? In other words if I zoom 6X is the object the camera sees larger by a true factor of 6x then what the eye sees?

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RE: Zoom magnification. 3x, 5x, 10x? What lens length... - 2/12/2005 8:38:59 PM   
Tall Paul



Posts: 4627
Joined: 6/23/2002
From: Palmdale, CA, USA
Status: offline 		No. What the eye sees has no relation to what a lens sees.
The "normal" lens for the 35mm film format is 50-55 mm., which has a field of view of 40 degrees on the long side, 27 degrees on the short side.
The eye has a nearly 180 degree field of view when considering the peripheral vision horizontally, and slightly greater than 90 degrees vertically.
"magnification-zoom" refer to the optics alone, it's a scale factor.
The smaller focal ratios of the digital camera, 5 to 8 mm reflect the small size of the imager chip.
An imager chip the size of 35mm film would have an astronomical cost.
And probably be outperformed by Kodachrome film anyway.

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